(a) Field of the Invention
The present invention relates to a liquid crystal display having wide viewing angle.
(b) Description of the Related Art
A liquid crystal display (LCD) includes two substrates and a liquid crystal layer interposed therebetween. The transmittance of the incident light is controlled by the strength of the electric field applied to the liquid crystal layer.
A vertically aligned twisted nematic (VATN) liquid crystal display has a couple of transparent substrates which have transparent electrodes on their inner surfaces and a couple of polarizers attached to their outer surfaces. The VATN LCD further includes a liquid crystal layer between the two substrates, and the liquid crystal layer has chirality and negative dielectric anisotropy.
In the off state of the LCD, i.e., in the state that no voltage is applied to the electrodes, the long axes of the liquid crystal molecules are aligned perpendicular to the substrates.
When the sufficient voltage difference is applied to the electrodes, an electric field perpendicular to the substrates and the liquid crystal molecules are rearranged. That is, the long axes of the liquid crystal molecules tilt in a direction perpendicular to the field direction or parallel to the substrates due to the dielectric anisotropy, and twist spirally with a pitch due to the chirality.
As described above, since the long axes of the liquid crystal molecules in the off state is perpendicular to the substrates, the VATN LCD having crossed polarizers may have sufficiently dark state. Therefore, the contrast ratio of the VATN LCD is relatively high compared with the conventional TN LCD. However, the viewing angle of the VATN LCD may not be so wide due to the difference in retardation values among viewing directions.
To overcome the above-described problem, multi-domain structures formed by varying rubbing directions in the alignment layers or by forming apertures in the transparent electrodes are proposed. Clere disclosed a structure having linear apertures in a transparent electrode in U.S. Pat. No. 5,136,407, and Hirose et al. disclosed an LCD using fringe fields to make the long axes of the liquid crystal molecules to be aligned in a direction between polarizing directions in U.S. Pat. No. 5,229,873. On the other hand, Lien proposed a structure having X-shaped apertures in a transparent electrode in U.S. Pat. No. 5,309,264, and Histake et al. disclosed a structure having apertures in both of the electrodes in U.S. Pat. No. 5,434,690.
However, the proposed structures may not have a sufficiently wide viewing angle and the luminance in their on states is not so high.